<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>

        // document.write(Math.floor(Math.random()*20 )+1)
        let r=3;
        let value = Math.PI * Math.pow(r,2);
        alert(Math.round(value *100)/100);
        // document.write()
</script>
</body>
</html>